$ { \left[\begin{array}{rrr}{-1} & {1} & {1} \\ {0} & {-2} & {0}\end{array}\right]+\left[\begin{array}{rrr}{1} & {3} & {-1} \\ {3} & {-1} & {2}\end{array}\right] = {?} } $
To find the sum of two matrices, add the corresponding items between each matrix. ${\left[\begin{array}{rrr}{-1}+{1} & {1}+{3} & {1}+{-1} \\ {0}+{3} & {-2}+{-1} & {0}+{2}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{rrr}{0} & {4} & {0} \\ {3} & {-3} & {2}\end{array}\right]}$